bitbake:hob: use a socks proxy mechanism for git

Instead of a custom git proxy mechanism, Hob now
uses a SOCKS proxy in order to work with external
repos via the oe-git-proxy helper script.

Fixes [YOCTO #4187]

Signed-off-by: Cristian Iorga <cristian.iorga@intel.com>
Signed-off-by: Cristian Iorga <ubik3000@gmail.com>
Signed-off-by: Cristian Iorga <cristian.iorga@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
hob:Only display scrolled list of images if needed

- do not set the Images window to always display a scroll bar if it is not needed

[Yocto #4171]
Signed-off-by: Ioana Grigoropol <ioanax.grigoropol@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>